The prior art predominantly describes amphoteric surface compounds that show no particular alkali stability. For example, sulfonic acid salts are the most common types of synthetic detergents described in the literature. Despite the fact that various synthetic surfactants exist for detergent applications, the need for acid- and alkali-stable surfactants remains.
The necessity for surface active agents that are stable in moderately strong alkali is discussed in U.S. Pat. No. 4,214,102. This patent teaches that many materials with amide linkages are destabilized in strong acids and alkalis, because that linkage readily breaks down in such media resulting in turbid solutions. The object of that invention is to develop amphoteric surface-active compounds that give a greater hydrophilic effect to the molecule and exhibit wide pH range stability from acidic to alkaline over long time periods. Those products are obtained by reaction of a glycidal ether with an excess of an N-hydroxy-C.sub.2-4 -alkyl-C.sub.2-6 -alkylene diamine and then N-alkylating the product with an excess of halo C.sub.2-4 alkanoic acid or halo C.sub.2-4 hydroxyalkane sulfonic acid.
Among the compounds produced are ones that have "the probable formulae": ##STR1## The products formed are shown to be good foamers and stable in both 20% sodium hydroxide and 20% sulfuric acid. However, the surface tension of 20% NaOH containing either 1% or 5% of the subject product was only reduced to 66.4 dyne/cm, indicating very poor surface activity in such a solution.
U.S. Pat. No. 3,839,318 describes the only commercial product that is stable in concentrated alkali solutions; it is sold under the trademark Triton BG-10 and comprises higher alkyl monosaccharides and higher oligosaccharides. Triton BG-10 is characterized by some deficiencies; namely, it is quite dark and viscous, has a burnt odor, only dissolves slowly in 50% NaOH, does not reduce the surface tension of 50% NaOH to any great extent, and produces foam.
U.S. Pat. No. 4,978,781 describes low-foam alkali-stable amphoteric surface active agents, including products of the formula: ##STR2## wherein R is selected from alkyl, aryl or alkylaryl groups of 4-18 carbon atoms or alkoxymethylene; wherein the alkoxy group contains 4-18 carbon atoms; R.sub.2 and R.sub.3 are individually selected from the group consisting of methyl, alkyl of 5-6 carbons, where said alkyl group is substituted by an electron-donating group on the beta carbon thereof, polyoxyethylene and polyoxypropylene; alternatively, R.sub.2 and R.sub.3 may together be --CH.sub.2 CH.sub.2 OCH.sub.2 CH.sub.2 -- or --CH.sub.2 CH.sub.2 SCH.sub.2 CH.sub.2 -- (i.e., together with nitrogen constitute a morpholine or thiomorpholine ring); M is hydrogen or an alkali metal cation; and X is hydrogen or an electron-donating group such as OH, SH, CH.sub.3 O or CH.sub.3 S. Those products are said to be compatible with aqueous solutions containing up to 50% NaOH, appreciably reduce the surface tension of such solutions, remain dissolved when the concentrate is diluted with water to use concentrations of 5-20%, generate little or no foam in solutions containing 50% or less NaOH, and remain unchanged upon extended boiling of such solutions containing 5-20% NaOH.